Cincy Science: That sinking feeling about sinkholes and why they happen where they happen

CINCINNATI - Ever ask, "What is that?" Or, "Why is that?" In our new "Cincy Science" feature, we talk with people who can answer those questions: The folks who do science in Cincinnati and the Tri-State.

In February, car enthusiasts cringed when they viewed footage of the massive sinkhole that swallowed eight classic cars at the Corvette Museum in Bowling Green, Ky.

WATCH: the security video

Nearly a year ago, a sinkhole of greater magnitude proved deadly when it consumed a south Florida man's bedroom while he slept.

Closer to home, there was the Norwood sinkhole last May . These stories both pointed to underground caverns as being the culprit, but what actually causes the caverns to form and are we at risk of more sinkholes in the Tri-State?

University of Cincinnati professor and archeological geologist Ken Tankersley explained why the ground gives way. He said caverns are essentially in his DNA, coming from generations of coal miners in southern Kentucky, and ancestors who lived above caverns in Yorkshire, England.

Q&A: What's the deal with sinkholes?

1. How common are sinkholes in that particular region by the Corvette Museum?

That area contains the largest cave system in the world which is Mammoth Cave National Park , and the national park is in eyesight of the museum. The reason the longest cave in the world is located there is because there’s a thick accumulation and just massive amounts of what we call Mississippian Age limestone.

2. What causes sinkholes like the one in Bowling Green?

What happens is, limestone is made of calcium carbonate, and if you’ve ever added vinegar to baking soda as a kid, the same thing happens in nature. Vinegar is an acid and the limestone is calcium carbonate, and when the rainwater hits the ground, it starts to mix with organic material such as leaves and the roots of plants and that creates an organic acid. As that percolates into the bedrock, it starts to dissolve the rock creating cracks on planes of weaknesses.

We know that the earth is constantly moving, and when the earth moves up and down, the limestone is brittle and it develops vertical cracks. Sometimes it cracks horizontally like pages in a book and those are called bedding planes. So these cracks are conduits for the percolating ground water which has a high acid content which literally starts to etch away the limestone. The same way a soft drink which has carbonic acid in it eats away at your teeth and you eventually get cavities.

3. So is that how underground waterways form?

Eventually the cracks get big enough that water will flow through it. And if the cracks are at the level of the water table, then you get underground lakes and rivers as is the case in the area of the Corvette Museum. They have flowing water. As dissolution continues from the bottom up where there’s water, it continues to dissolve the limestone until it reaches the surface and that creates the sinkhole.

4. Are sinkholes a potential threat in the Greater Cincinnati area?

If you drive around the Cincinnati area, it’s quite different. You see very thin layers of limestone with very thick layers of shale--which is derived from clay--so we get a lot of landslides, but not sinkholes. You don’t want to build on a hill around here because the ground does slip, but not because of underground caves.

5. Why do some areas have higher concentrations of limestone underground?

These are sediments that were deposited by ancient seas, hundreds and millions of years ago. Even the limestone around here is around a half a billion years old. It’s when there was a shallow epicontinental sea. If you think about seas and very shallow deposits near shore, you get organic deposits that eventually become coal. A little deeper, but still shallow you get sand deposits. But if you go out to the deep waters, you get a very fine accumulation of calcium carbonate.

“Where does that come from? Well, it actually comes from organisms that lived in the seas in the past, things like Brachiopods, Cephalopods and Bryozoan – all of these species have shells and exoskeletons made of calcium carbonate and they contribute and accumulate and essentially form this massive amount of limestone. They’re a testament to time, but also they show what the ocean was like at the time of their deposition.

6. What regions of the country are sinkholes most likely to develop?

Anyone living on a Karst landscape, places like northern Florida, northern Tennessee, northern Georgia, northern Alabama and a good part of Kentucky--not northern Kentucky, but southeastern Kentucky and south-central Kentucky, there’s a risk of having a building on top of a cave system. There are geophysical methods where you can tell whether or not the cave is underground, but very few people go into that detail before they go into construction activity.

Karst landscape is the environment created by dissolving limestone including caverns, sinkholes and dramatic land features.

7. Where can you see good examples?

You can see examples in southwestern

Kentucky and south-central Kentucky going on into what we call the TAG region – Tennessee, Alabama and Georgia. This Karst landscape occurs and if you fly over it, it’s literally peppered with sinkholes. You can see some of them are filled with water that intercepts the water table and others go straight into deep caverns. Some of them are upwards of 500 feet deep. The one in underneath the Corvette Museum comparatively is quite shallow.”

8. Are we as humans increasing the probability of sinkholes?

Acid occurs naturally through rain water. These days we’re seeing that with our fossil fuels both the burning of gasoline and the burning of coal increases the amount of acidity. So we’re actually hastening the process.

9. Where can people go locally to get a more in-depth view of caverns?

North, you have Indian Trail Caverns which has the oldest evidence of humans going underground in the western hemisphere during the Ice Age and then to the south of us going about the same distance you have Mammoth Cave, the longest cave in the world.

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